1. Field of the Invention
The present invention relates to a method of producing a liquid ejection head for ejecting liquid.
2. Description of the Related Art
An ink jet recording head employed in an ink jet recording method, in which recording is performed by ejecting ink onto a recording medium, is a typical liquid ejection head. An ink jet recording head usually includes an ink flow path, ejection-energy generating elements provided at a part of the flow path, and fine ink-ejection ports through which ink is ejected by the energy generated by the ejection-energy generating portions.
Japanese Patent Publication No. 2-24220 discloses a method of producing a liquid ejection head, which can be applied to the production of an ink jet recording head. In the method disclosed therein, a side wall of a liquid flow path is formed on a substrate having a plurality of ejection-energy generating portions so as to enable communication with the outside at a position near the circumference of the substrate and so as to enable liquid to be supplied therefrom into the flow path. Then, a photoresist layer forming a ceiling of the flow path is laminated thereon, and the photoresist on a space serving as the flow path is exposed, heated, and cured. Finally, unexposed portions of the photoresist are removed to provide ejection ports in the photoresist.
United States Patent Application Publication No. US2007/0070122 discloses a method in which a liquid supply port is processed on the surface of a substrate having a liquid supply port penetrating from the surface to the back surface of the substrate to form a side wall of the flow path. Then, a photoresist layer is laminated thereon, and ejection ports are provided in the photoresist layer, at positions above the space that eventually serves as the flow path.
In the method disclosed in Japanese Patent Publication No. 2-24220, when the ejection ports are provided in the photoresist layer, gas in the space that eventually serves as the flow path is heated by the heat after the exposure and expands. However, because the flow path communicates with the outside air at the circumference of the substrate, the gas can be discharged. Also in the method disclosed in United States Patent Application Publication No. US2007/0070122, the expanded gas can be discharged through the supply port to the back surface of the silicon substrate. By efficiently discharging gas, the photoresist layer can be prevented from being deformed by the expanded gas.
However, because the supply port is provided at a side end of the substrate in the structure of the liquid ejection head disclosed in Japanese Patent Publication No. 2-24220, with a long liquid ejection head, liquid refilling characteristics may vary depending on the distance between the supply port and the ejection ports.
On the other hand, with the method disclosed in United States Patent Application Publication No. US2007/0070122, because the substrate having the opening is weak, the substrate may be deformed by the stress applied thereto when the photoresist layer is formed thereon. In addition, forming a flat layer on the substrate surface having an opening is difficult. Thus, a special flattening process may be required.
As has been described, with the conventional techniques, the gas expanded by the photolithography can be discharged from the supply port. However, the ejection performance of the head and the production process are limited.